1. Field of the Invention
The present invention relates generally to the art of forming rings using processes generally known as ring rolling and drum rolling, and more particularly to forming such rings which have a pattern of stiffening elements integrally formed on their outer surfaces. Still more specifically, the invention relates to the tooling and drum components for preparing such rings. The rings produced by the process of the present invention represent unique articles which themselves are part of the invention.
2. Description of Related Art
Since the present invention employs certain aspects of known processes, this background will begin with a brief description of current ring and drum rolling processes. Such processes are employed with high and low density alloys, to form continuous, seamless rings in a variety of sizes and for numerous applications. The process typically begins with a solid raw material heated to forming temperature and subsequently upset in a press to a generally cylindrical shape of appropriate size. In most prior art processes, the blank is then placed into a pot die and back extruded with a punch into a hollow cylindrical shape. This cylinder is then conditioned and ring rolled in one or several steps, during which a bearing mounted roll pushes the cylinder between itself and a rotating drive roll. Pinch and guide rolls are also frequently involved to insure proper final geometry. As the pressure is increased, the wall thickness of the cylinder decreases, resulting in an increase in ring diameter. Various heating steps and the use of various initial and finishing ring rolls can be employed, as is generally known in the art.
Many shapes and sizes of rings can be produced using this process. Universal, cylindrical tooling (mandrel ring rolls and drive rolls) are used to prepare cylindrical, smooth rings, or the tooling can be contoured to produce rings with circumferential ribs in the inside or the outside of the cylinder. Such ribs are concentric due to the nature of the rolling process.
A variation of the ring rolling process just described is known as drum rolling and is used when it is desired to obtain tightly controlled shapes and geometries. The process differs from ring rolling in that the cylinder to be formed is placed inside a rigid, generally cylindrical drum, and that combination is then placed over the rolling mandrel. The cylinder is rolled so that its diameter increases to a designated point and completely fills the inside of the rigid drum. If it is then desired to produce external contours using the drum process, the drum or mandrel can be provided with protrusions or recesses, again in patterns which are concentric with the axis of the drum.
Rings produced by the ring and drum rolling processes can be used for many applications and can be prepared in sizes ranging from a few feet to more than twenty feet. Such rings may be employed, for example, as components of pressure vessels of the type used in aerospace equipment for containing hydrogen or oxygen. Critical design limitations for such applications include weight and strength. One way to accommodate the weight issue is to use lightweight alloys, such as aluminum alloys, titanium alloys or the like. It has also been suggested that stiffening ribs can be used for added strength and weight reduction, but prior to the present invention the formation of effective integrally formed stiffening rib patterns has not been achieved. The machining of such patterns into the outside of smooth cylinders has been attempted, but such processing is extremely time consuming and is very expensive. Moreover, it is difficult to achieve the type of precision which is required using such simple machining technology. It would represent a very substantial advance in the art of making integral ribs stiffened rings to be able to accurately produce integral rib stiffening elements in the outer surface of such rings in an efficient and cost effective manner. It would also be highly advantageous to be able to provide a variety of patterns for the integral ribs, not just concentric patterns, but patterns which include ribs which are parallel to the ring axis, or slanted in any desired pattern.